
// 判断obj是否为一个整数
let isInteger = (obj) => {
    return Math.floor(obj) === obj
}
/*
 * 将一个浮点数转成整数，返回整数和倍数。如 3.14 >> 314，倍数是 100
 * @param floatNum {number} 小数
 * @return {object}
 *   {times:100, num: 314}
 */
let toInteger = (floatNum) => {
    var ret = { times: 1, num: 0 };
    if (isInteger(floatNum)) {
        ret.num = floatNum;
        return ret
    }
    var strfi = floatNum + '';
    var dotPos = strfi.indexOf('.');
    var len = strfi.substr(dotPos + 1).length;
    var times = Math.pow(10, len);
    var intNum = parseInt(floatNum * times + 0.5, 10);
    ret.times = times;
    ret.num = intNum;
    return ret
}
/*
 * 核心方法，实现加减乘除运算，确保不丢失精度
 * 思路：把小数放大为整数（乘），进行算术运算，再缩小为小数（除）
 *
 * @param a {number} 运算数1
 * @param b {number} 运算数2
 * @param op {string} 运算类型，有加减乘除（add/subtract/multiply/divide）
 *
 */
let operation = (a, b, op) => {
    var o1 = toInteger(a);
    var o2 = toInteger(b);
    var n1 = o1.num;
    var n2 = o2.num;
    var t1 = o1.times;
    var t2 = o2.times;
    var max = t1 > t2 ? t1 : t2;
    var result = null;
    switch (op) {
        case 'add':
            if (t1 === t2) { // 两个小数位数相同
                result = n1 + n2
            } else if (t1 > t2) { // o1 小数位 大于 o2
                result = n1 + n2 * (t1 / t2)
            } else { // o1 小数位 小于 o2
                result = n1 * (t2 / t1) + n2
            }
            return result / max;
        case 'subtract':
            if (t1 === t2) {
                result = n1 - n2
            } else if (t1 > t2) {
                result = n1 - n2 * (t1 / t2)
            } else {
                result = n1 * (t2 / t1) - n2
            }
            return result / max;
        case 'multiply':
            result = (n1 * n2) / (t1 * t2);
            return result;
        case 'divide':
            result = (n1 / n2) * (t2 / t1);
            return result
    }
}
// 加减乘除的四个接口
export const add = (a, b) => {
    return operation(a, b, 'add')
}
export const  subtract = (a, b) => {
    return operation(a, b, 'subtract')
}
export const  multiply = (a, b) => {
    return operation(a, b, 'multiply')
}
export const  divide = (a, b) => {
    return operation(a, b, 'divide')
}
export const  decimalsNum=(data,num)=>{
    if(!data||!num)return data;
    let text = data.toString()
    let dIndex=text.indexOf('.')
    if(dIndex==-1){
        return text+'.00';
    }else{
      return  text.slice(0,dIndex+num+1)
    }
}
export default{
    add,
    subtract,
    multiply,
    divide,
    decimalsNum
}
